Method and arrangement for controlling the power of a transmission amplifier

ABSTRACT

A method and arrangement for controlling the power of a transmission amplifier reliably within as wide a power band as possible, for a desired transmission power level which is less than a predetermined limit value. In the present invention, a portion of the power emitted from the transmission amplifier is output through a switching device in addition to the power which is output through a directional coupler, and is used to control the transmission amplifier.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a method and an arrangement for controlling thepower of a transmission amplifier, in particular of a transmissionamplifier in a mobile radio terminal.

FIG. 3 shows an outline circuit diagram of a conventional arrangementfor controlling the power of a transmission amplifier PA. The signalssig which are supplied to the transmission amplifier PA and are to beamplified are amplified on the basis of a control parameter reg, whichis supplied to the transmission amplifier PA and represents a measure ofthe gain or the gain level/factor, and are supplied to a directionalcoupler RK. The directional coupler RK outputs a small portion of thepower supplied from the transmission amplifier PA to the antenna ANT andsupplies it to a radio frequency detector HFD, which converts this powerinto a DC voltage. This DC voltage value produced in this way issupplied as an actual value—(act)—to a comparison device V, where it iscompared with a nominal value—(nom)—which is predetermined by a controldevice, such as a microcontroller in a mobile radio terminal. Thecomparison results in a control parameter reg being output, which setsthe gain of the transmission amplifier PA such that the actual valuecorresponds to the nominal value nom. To this end, the gain factor israised or lowered based on the difference between the nominal value andthe actual value. The majority of the power is supplied from thedirectional coupler RK to the antenna ANT, from which this power istransmitted in the form of radio-frequency signals. Such conventionalpower control loops for a transmission amplifier operate well over anarrow predetermined power band.

However, in order to improve the spectrum utilization and to increasethe operating time of the mobile radio appliance, modern mobile radioterminals can be operated at different transmission power levels. Forexample, depending on the power class of the mobile radio terminal, thetransmission power of GSM (Global System for Mobile Communication)mobile radio terminals can be varied within a range of 20 and 30 dB.Furthermore, the transmission power of mobile radio terminals whichoperate using a time slot mode, such as GSM mobile radio terminals, mustbe controlled on the basis of a predetermined time slot structure. Inthis case, it is particularly important in order to produce atransmission pulse (burst) to set the transmission amplifier inaccordance with a fixed predetermined nominal time/power curve (powerramping), which likewise necessitates a wide power dynamic range.

These two requirements for controlling the power of a transmissionamplifier can no longer be satisfied reliably by conventional methods orarrangements. In particular, reliable power detection by means of an RFdetector over a wide power band is scarcely feasible using simple means.This problem is further exacerbated when controlling the power of amultiband or multimode mobile radio terminal since, in this case, thenumber of transmission power levels is further increased, and differentnominal time/power curves can be specified. Future CDMA mobile radioterminals will also require transmission power control over a very widepower band.

SUMMARY OF THE INVENTION

The invention is thus based on the object of specifying a method andarrangement for controlling the power of a transmission amplifier, whichallow the power to be controlled in a simple manner and neverthelessreliably over a wide power band. According to the invention, a portionof the power emitted from a transmission amplifier is output by means ofa coupling element, and for a desired transmission power level, which isless than a predetermined limit value, a further portion of the power isadditionally output by means of a controlled switching device, and theoutput power is used for controlling the transmission amplifier.

The invention is accordingly based on the idea of outputting arelatively small portion of the power by means of a coupling element ina first case in which the desired transmission power is greater than apredetermined limit value, and of using this small portion to controlthe power of the transmission amplifier. In a second case, in which thedesired transmission power is below a specific limit value, a relativelylarge portion of the power emitted from the transmission amplifier isadditionally output via a switching device, and is used to control thepower of the transmission amplifier.

This means that, in both cases, the absolute value of the output poweris at least in a similar order of magnitude, and the components whichare used for further processing the output power to form a controlparameter for the transmission amplifier, in particular theradio-frequency detector, can thus be operated in a relatively narrowband, thus ensuring that the power can be controlled more reliably andwith less complexity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an outline circuit diagram of one embodiment of anarrangement for controlling the power of a transmission amplifier.

FIG. 2 shows an outline circuit diagram of one embodiment of anarrangement for controlling the power of a transmission amplifier.

FIG. 3 shows an outline circuit diagram of a conventional arrangementfor controlling the power of a transmission amplifier.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a transmission amplifier PA which amplifies the signalssig, which, for example, are output from the radio-frequency section HFof a mobile radio terminal, based on a control parameter reg which islikewise supplied to the transmission amplifier PA, and which outputs apower level corresponding to this control parameter reg.

In a first case, in which the desired transmission power, for examplethe desired power step or the maximum power which can be emitted fromthe transmission amplifier or from the antenna during operation of themobile radio terminal in this power step, is greater than apredetermined limit value, the switching device S, which is controlledby a control device STE (such as the microcontroller in a mobile radioterminal) and may be, for example, in the form of a transistor, isopened, so that only a relatively small portion of the power emittedfrom the transmission amplifier PA is output through a coupling element,such as a directional coupler RK, and is supplied to a power detector,such as a radio-frequency detector HFD. The radio-frequency detector mayalso be in the form of a diode or a transistor. The other relativelylarge portion of the power is supplied to an antenna ANT, from which itis transmitted. The radio-frequency detector HFD converts the outputpower to a DC voltage signal which is supplied as an actual value to acomparison device V, which may be in the form of a differentialamplifier circuit. This actual value is compared there with a nominalvalue nom, with a control parameter reg being output as the result ofthe comparison, which is set in such a manner that the signals emittedfrom the transmission amplifier are at a power level which correspondsto the desired transmission power; this is the situation when thenominal value nom corresponds to the actual value act.

The nominal value nom in this case corresponds to the currently desiredpower value on a nominal time/power curve, which can be stored in amemory device SPE, for example a read only memory, and can be selected,read, and, if necessary, adapted or processed by the control device STE,for example a microcontroller in a mobile radio terminal. Thecorresponding value is then supplied as the nominal value nom to thecomparison device V.

In a second case, in which the desired transmission power level is lessthan a predetermined limit value, the controlled switching device S isclosed and a relatively large portion of the power emitted from thetransmission amplifier PA is output through the switching device S. Thisoutput power is supplied to the radio-frequency detector HFD togetherwith the relatively small, possibly negligible, proportion of the powerwhich is output through the directional coupler RK and, after conversionto a DC voltage, is supplied as the actual value act to the comparisondevice V.

When the switching device S is closed, a considerably greater absolutevalue of the power is output for power control, and can thus not besupplied to the antenna. In order to continue to supply the desiredtransmission power level to the antenna, the gain through thetransmission amplifier is correspondingly increased. For this purpose,the switch position of the switching device S can also be taken intoaccount as follows: the nominal value nom is either determined on thebasis of different nominal time/power curves read from the memory deviceSPE, or on the basis of a standard nominal time/power curve which, oncethe corresponding values have been read, can be further processed andadapted by the control device STE depending on the switch position.

When the invention is used in a multimode or multiband terminal, thepower control adaptation to the present power step or the presentnominal time/power curve can likewise be carried out by selection of thecorresponding nominal time/power curve or by adaptation of a standardnominal time/power curve by means of the control device.

In order to illustrate the exemplary embodiments clearly, the drawingsdo not show duplexers, diplexers, matching or converter circuits.

FIG. 2 shows one design variant of the invention, which differsessentially from the exemplary embodiment illustrated in FIG. 1 in thatthe controlled switching device S is not arranged between thetransmission amplifier PA and the coupling element RK, but between thecoupling element RK and the antenna ANT. In this case, the two designvariants operate essentially in the same way.

Although other modifications and changes may be suggested by thoseskilled in the art, it is the intention of the inventors to embodywithin the patent warranted hereon all changes and modifications asreasonably and properly come within the scope of their contribution tothe art.

What is claimed is:
 1. A method for controlling power of a transmissionamplifier, comprising the steps of: outputting a first portion of apower being emitted from a transmission amplifier via a directionalcoupler before the power is supplied to an antenna; further outputting asecond portion of the power being emitted from the transmissionamplifier via a control switching device, provided that a desiredtransmission power level for the transmission amplifier is less than apredetermined value, an input for said control switching device beinglocated between the directional coupler and one of the transmissionamplifier and the antenna, an output for said control switching devicebeing located between the directional coupler and a device forcontrolling the power of the transmission amplifier, said furtheroutputting step for obtaining a desired transmission power level; andsetting a gain factor of the transmission amplifier by utilizing asignal that is dependant on a total output power of the transmissionamplifier.
 2. A method according to claim 1, further comprising thesteps of: supplying the signal to a comparison device, said signalcorresponding to an actual value; further supplying a nominal value tothe comparison device, said nominal value corresponding to a nominalpower level, said nominal value being determined as a function of aposition of the control switching device; comparing the actual valuewith the nominal value via the comparing device; and setting the gainfactor of the transmission amplifier based on a result of said comparingstep.
 3. An arrangement for controlling the power of a transmissionamplifier comprising: a transmission amplifier; a device for controllingthe power of the transmission amplifier; a directional coupler foroutputting a portion of a power emitted from the transmission amplifierbefore said power is being supplied to an antenna; and a controlswitching device for further outputting a further portion of the poweremitted from the transmission amplifier, provided that a desiredtransmission power for the transmission amplifier is being less than apredetermined limit value, said control switching device having an inputlocated between the directional coupler and one of the transmissionamplifier and the antenna, an output of said control switching devicebeing located between the directional coupler and the device forcontrolling the power of the transmission amplifier.
 4. An arrangementaccording to claim 3, further comprising; a comparison device forcomparing a nominal value with an actual value and for outputting acomparison result, said comparison device being supplied with a signalcorresponding to the actual value, said signal being dependent on atotal output power of the transmission amplifier, said comparison devicebeing further supplied with a nominal value, said nominal valuecorresponding to a nominal power level; and a device for determining thenominal value as a function of a position of the control switchingdevice.